All going broody - stressed new member grateful for help

We are new to poultry.
Was intended to be a bit of fun for the kids and it is.
We have 4 x 5 day old chicks (orpington bantam x hamburg) and doing really well. Mom is very loyal and attentive.
This wasn't deliberate we found her having thought she was lost to a predator.

We now have a broody blue menorca and a leghorn x.

I have access to packing cases made of wood at work which are thrown into general waste after delivery of goods inside.

They are 30"h x 20"w x25"d. I can easily fit ventilation to these and hinge the front panel to make it a door with a wire mesh viewing panel.
If we want to hatch using broody hens are these sufficient in size.